Highly-Resilient, Energy-Efficient Multipath Routing in Wireless Sensor Networks Deepak Ganesan UCLA deepak@cs.ucla.edu Ramesh Govindan USC-ISI govindan@isi.edu Scott Shenker ACIRI shenker@aciri.org Deborah Estrin UCLA destrin@cs.ucla.edu ABSTRACT Previously proposed sensor network data dissemination schemes require periodic low-rate flooding of data in order to allow re- covery from failure. We consider constructing two kinds of multipaths to enable energy efficient recovery from failure of the shortest path between source and sink. Disjoint multipath has been studied in the literature. We propose a novel braided multipath scheme, which results in several partially disjoint multipath schemes. We find that braided multipaths are a vi- able alternative for energy-efficient recovery from isolated and patterned failures. 1. INTRODUCTION Sensor networks [2] are envisaged as large-scale networks of small networked sensor nodes such as the Rene [4]. Such a node could have one or more sensors and would be densely deployed near the phenomena to be sensed, in a highly redun- dant manner to maximize lifetime, and deal with dynamics and failures. Three criteria drive the design of large-scale sensor net- works: scalability (these networks might involve thousands of nodes), energy-efficiency (in particular, wireless communi- cation can incur significantly higher energy cost than compu- tation [7]), and robustness (to environmental effects and node and link failures). These networks may require novel routing techniques for scalable and robust data dissemination, such as Directed diffu- sion [5]. Of particular interest is the notion of path reinforce- ment; that a node in the network may make a local decision (based possibly on perceived traffic characteristics) to draw data from one or more neighbors in preference to other neigh- bors. We say that such path setup techniques use localized algorithms. In this paper, we propose using multipath routing to in- crease resilience to node failure. We explore localized algo- rithms for two different approaches to constructing multipaths between two nodes. One is the classical node-disjoint multi- path adopted by prior work, where the alternate paths do not intersect the original path (or each other). The other approach abandons the requirement for disjoint paths and instead builds many braided paths. With braided paths, there are typically no completely disjoint paths but rather many partially disjoint alternate paths. We use two important metrics in judging the performance of these competing approaches, resilience and maintencance overhead There is an inherent tradeoff between these two quan- tities. Becoming more resilient typically consumes more en- ergy. In this paper we investigate the tradeoffs that result from the two proposed routing algoirthms. 1 The literature on multipath routing is vast and we do not attempt to be comprehensive in this summary of related work. To our knowledge, however, ours is the first attempt to evaluate the energy/resilience tradeoff for multipath routing in wireless sensors. Some of our design choices have been influenced by Dispersity Routing [1] and work on multipath in ad-hoc net- works [6] 2. DISJOINT AND BRAIDED PATHS Classical multipath routing has been explored for two rea- son: load balancing and robustness. While load-balancing is essential to conserve energy in sensor networks, this is not the focus of our paper. Instead, we use multipath routing to rapidly find alternate paths between source and sink. Our rationale for this use of multipath is as follows. We assume that, from the application’s perspective, a desirable goal is to deliver data along this primary (best available) path. However, to scalably (i.e. without flooding for rediscovery) recover from failure of this primary path, we construct and maintain a small number of alternative paths. Maintaining alternate paths, however, in- cur the overhead of sending low-rate data through alternate paths as keep-alives and does not preclude the pathological case of failure on all multipaths. We consider two designs for multipath routing: disjoint(Section 2.1) and braided (Section 2.2). The energy- resilience tradeoffs of these schemes are then explored via simulation(Section 4). 2.1 Disjoint Multipaths The first multipath mechanism we consider constructs a small number of alternate paths that are node-disjoint with the pri- mary path, and with each other. These alternate paths are thus This paper provides a flavor of the multipath techniques sug- gested. Due to space constraints, some of the more detailed simulations and analysis has been omitted. 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